Electrostatic transfer copying machines that form images on a copy sheet require that the transported copy sheet be accurately guided to the transfer station. Guiding apparatus such as that shown in FIG. 1 are used in conventional copying machines. That is, upper and lower guide panels a and b are disposed between a pair of rollers c and the transfer station d so as to be arranged in one direction and an opposite direction relative to the natural sheet feed path e (the path along the common tangential line through the nip portion of the pair of rollers c) formed by said pair of rollers c. The pair of guide panels a and b are arranged so as to confront one another such that the back ends thereof facing the pair feed rollers are substantially separated from the copy sheet feed path e, and the front ends thereof facing the transfer station converge toward the copy sheet feed path e.
Thus, by substantially separating the back ends of the pair of guide panels a and b, the leading end of the copy sheet g fed from the pair of feed rollers c can be readily received between the pair of guide panels a and b even if the feed direction changes in sheet transport direction caused by changes in material, thickness, curling and direction of curling of the copy sheet g. Since the spacing interval between the front ends of the pair of guide panels a and b is narrow, the received copy sheet g is advanced at a predetermined angle into the sheet transport path e of the image bearing member f and the transfer station d so as to suitably adhere the copy sheet g to the surface of the image bearing member while advancing toward the transfer station d.
In the conventional apparatus shown in FIG. 1, the copy sheet g is transported along the feed path e from the pair of feed rollers, and is forcibly bent from the bottom side as the sheet advances toward the image bearing member f and the transfer station d. Therefore, when the trailing end of the copy sheet g leaves the pair of rollers c, the trailing end of the sheet g becomes free of said pair of rollers and rebounds upwardly in a self-righting action to assume its natural state. The aforesaid upward rebound of the trailing end of the copy sheet g is more pronounced with sheets having greater stiffness due to the material or thickness of the sheet, and produces undulation of the copy sheet g during the transfer. This undulation adversely affects the transfer by causing transfer dislocation, which reduces image quality.
When the spacing interval between the pair of guide panels a and b is narrowed to compensate for the aforesaid undulation, it becomes difficult to receive the copy sheet fed from the pair of rollers c, thereby causing paper jams. In the above description, a spring applies a force on the lower guide panel from the upper guide panel side so allow responsiveness to differences in passage resistance produced by variations in sheet thickness. To allow accurate receiving of the copy sheet sent from the pair of rollers, the back end sides of the pair of guide panels are substantially separated such that the upward rebound of the trailing end of the copy sheet cannot be prevented. Particularly when the trailing end of the copy sheet is released from the pair of rollers and enters the free state, the lower guide panel actively raises the aforesaid trailing end of the sheet and readily undulates due to the action of the spring. Thus, the previously describe disadvantages are not eliminated.